The DNA repair factor ku80 binds and activates the adhesion receptor ELTD1/ADGRL4

We investigated the mRNA expression of G protein-coupled receptors (GPCRs) in cells from four human vascular beds: umbilical vein (HUVEC), microvasculature (MVEC), aorta (HAEC), and coronary artery (CAEC). Our study revealed that the orphan receptor ELTD1 (ADGRL4) was the most abundantly expressed GPCR mRNA in all four EC types. When recombinantly expressed in U87 cells, ELTD1 receptors activated canonical GPCR pathways, particularly the Gq pathway. Conditioned medium from U87 cells also activated ELTD1 in HEK293 cells, supporting the existence of an autocrine ELTD1-activating factor. Using affinity capture and mass spectrometry in combination with the label free xCelligence system, we identified the proteins ku80 and erythrocyte beta spectrin (SPTB) as ligands to ELTD1. Ku80 demonstrated higher potency in activating ELTD1 than SPTB, thus leading us to focus on this protein. INCA-X, a functional antibody targeting the ku80/ku70 complex, and ELTD1 siRNA impaired endothelial tube formation in a similar manner, suggesting a common pathway. In a study cohort of myocardial infarction patients, high plasma levels of the extracellular domain of ELTD1 correlated (P < 0.05) with high (>2.9) cardiovascular flow reserve, thus indicating an association between ELTD1 and active angiogenesis and revascularization.